Fatty acid screen vehicles



United States Patent FATTY ACID SCREEN VEHICLES William C. Morris, Mayfield Heights, Ohio N Drawing. Application June 6, 1957 Serial No. 663,890

6 Claims. (Cl. 106-19) This invention relates to vehicles employed in ceramic pastes. More particularly, the invention relates to vehicles of the fatty acid type and to an additive therefor. Specifically, the invention relates to a hot screen fatty acid vehicle and to the use of azelaic acid therein.

According to my invention I have discovered that azelaic acid imparts certain highly desirable properties to fatty acid type vehicles utilized for the application of vitrifiable ceramic compositions to base objects according to the hot squeegee techniques. The addition agent is particularly suited for use with fatty acids having a car- 'bon content ranging from about 12 to 22 carbon atoms. Suitable acids are, for example, lauric, myristic, palmitic, stearic, arachidic and behenic acids.

Generally the application of ceramic colors or ceramic paints to base objects is old in the art. For years ceramic decorations have been made by application of suitable paints by such means as brushing or spraying. The painted object is thereafter fired to volatilize or burn off the vehicle and to fuse the vitrifiable constituents to the base objects.

Recent innovations directed to the application of the vitrifiable ceramic compositions to base objects such as metal or ceramic containers have been founded upon the utilization of a screen stencil which is usually made from silk or metal. The screen is suitably blanked off according to the particular design and the ceramic paint is applied to the base object through the unblanked screen portions by means of a squeegee.

The so-called squeegee or screen process has been developed on the basis of what may be termed conventional and hot type application techniques. The former tech nique consists of suspending the vitrifiable ceramic material together with pigments and other additives in suitable viscous oils and then applying the paint by means of a squeegee and screen stencil to the base object. This technique results in a paint application which is wet and requires drying prior to further handling or superimposed color applications. To eliminate the necessity for drying to further handling or multi-color applications, the hot screen squeegee technique has been developed. This tech-' nique employs a thermoplastic vehicle which is solid at the temperature of the base object (normally room temperature), the vehicle being heated to a higher temperature during the actual application thereof to the base so as to provide suitable flow characteristics. This hot technique is carried out by maintaining the paint or paste in a fluid or semi-fluid condition during the application thereof to the base object. This is accomplished by means of radiant heat or by passing a current through the screen. In this manner, the paint or paste is maintained at a suitable consistency during the stenciling process and solidifies almost instantaneously after application because of the relatively lower temperature of the base object. It is apparent that the hot screen application technique is based principally on the use of a vehicle which has the characteristic of being fluid or semi-fluid at a temperature slightly in excess of the temperature of the base object "ice so that solidification thereof takes place on the base once the paint is applied thereto.

This invention is directed to a vehicle containing azelaic acid which may be employed for hot screen applications wherein the fundamental constituent of the vehicle is one or more fatty acids having from 12 to 22 carbon atoms. Occasionally it may be desirable for the azelaic acid to exceed the amount of fatty acid present therein. However, the fundamental constituent in the vehicle, that is the fatty acids, usually and preferably exceed 35% by' weight of the vehicle.

Vehicles of the fatty acid type heretofore mentioned that contain azelaic acid as an additive have been found to print flatter with fewer screen marks in the unfired condition than customarily resulting from similar vehicles not em loying the novel additive. It is believed that the azelaic acid promotes an after flow effect between the printing and the firing steps which substantially diminishes the predominance of screen marks. Still further, the azelaic acid containing vehicles appear somewhat to further minimize screen marks during the initial stages of firing through flow out during the preheating steps. It has also been found that the fatty acid vehicles incorporating the novel additive of my invention receive second colors in rnulti-color applications extremely well, for example without the loss of detail frequently encountered with other similar fatty acid vehicles. Furthermore, this reception characteristic for the second color has been found to exist when the second color is applied by either conventional or hot application methods. Other benefits derived from the use of my novel additive reside in exhibiting good film strength without undue brittleness and compatability with materials such as the plasticizer and wetting agents normally employed for adjusting the fundamental vehicle properties.

It is an object of the invention to provide an additive for fatty acid vehicles utilized for the application of ceramic materials to base objects by means of the hot screen techniques. A further object is to provide a vehicle including an additive which tends to eliminate screen marks. Other and further objects will be apparent from the following description.

According to the invention, azelaic acid imparts the aforementioned desired characteristics to vehicles wherein fatty acids form the fundamental constituent thereof. The same benefits appear unattainable when the fundamental vehicle constituent is an alcohol of the fatty acid type or one of the well known waxes.

Fatty acids having a number of carbon atoms falling from 12 to 22 such as lauric, myristic, palmitic, stearic, arachidic and behenic acids alone or combinations thereof may be employed as the fundamental constituent. Preferably the fatty acid in the vehicle is employed in amounts less than about by weight of the vehicle. Optimum amounts of the fundamental constituents range between about 50 and 70% by weight of the vehicle.

The azelaic acid may be employed in amounts up to about 55% by weight of the vehicle, the optimum printing property being usually obtained when employed in amounts from about 10 to 35% by weight of the vehicle. Noticeable improvements will usually be observed when the azelaic acid is employed in amounts as low as 0.5% by weight of the vehicle and good results have been obtained when azelaic acid is employed in an amount of about 5% by weight of the vehicle.

The azelaic acid may be utilized as the only modifying constituent or employed with other modifying agents to obtain suitable results. Thus modifiers such as viscosifiers, plasticizers, waxes, may be suitably incorporated to impart their characteristic properties where desirable. For example, viscosifiers such as ethyl cellulose or benzylcellulose have been found in some instances to impart aerasae is employed from about 2 to 7% by weight of the vehicle.

The ethyl cellulose has been found particularly beneficial in facilitating the handling of the paints containing the novel additive. In this "regard the various forms of ethyl cellulose commercially available have been found ade quate. It is preferable, however, to utilize those forms having a viscosity ranging between about 10 cps. and 300 cps. as determined in an 80:20 toluenezethanol solution and having about a 50% ethoxy substitution. Benzyl cellulose may be employed in similar amounts.

Where desirable, the well known waxes may also be incorporated to impart greater viscosity during the initial firing operations so as to prevent running of the paint during this period. Suitable waxes either synthetic or natural such as ceresine, candelilla wax and sugar cane wax may be employed. The waxes may be utilized in amounts up to about 35% of the vehicle although opti mum results appear to be attainable in amounts ranging from about 15 to 25% by weight of the vehicle. Similarly, suitable plasticizers such as hercolyn, a hydrogenated methyl ester of rosin, ester gums or synthetic resins may be employed preferably in amounts ranging from about to 20% by weight of the vehicle. Amounts of the plasticizers ranging from about 7 to 12% by weight of the vehicle generally producing optimum results. Obviously other modifiers may be employed without departing from the scope of the invention.

Of the vitrifiable compositions customarily employed in ceramic applications, the low melting fluxes such as lead borosilicates, modified lead borosilicates, etc. are most generally used. Addition agents are also frequently employed such as zirconium oxide (ZrO to impart alkali resistant properties thereto. Pigments obviously are usually utilized to impart the proper color to the I vitrified material. Typical pigments or ceramic colors may be TiO cobalt blue, and brown oxides. Other pigments may be utilized in combination with the vitrifiable ceramic compositions to impart the desired color to the final glaze.

Although the vehicles of the instant invention may be employed in various amounts with respect to the enamel constituents, generally, the employment of from about 15 to 40% of the vehicle or from about 85 to 60% of the enamel constituents is customary in compounded ceramic paints or pastes.

In compounding the ceramic paints or pastes, the fatty acids and azelaic acid together with such modifiers as it may be desirable to employ are first melted together until homogeneous, then mixed with the enamel constituents on a paint mill. The mixing is customarily carried out at a temperature about the same as that required for the hot screen application. For example, the mixing may be suitably carried out between about 55115 C. depending upon the consistency of the paint desired and the particular ingredients employed.

After mixing the ingredients, the paste or ceramic paint is transferred to the screen stencil which may be maintained at a temperature ranging from about 5 to C. above the temperature of the paste. The screen may be suitably heated by passing a current therethrough. Commercially the screen temperatures between about 60 and 120 C. are employed in the resistance heating versions of the hot screen technique. Another method of heating theconstituents during the paint application according to the hot technique is by radiant heat. The ceramic paint is applied to the base by drawing a squeegee over the scieento force the paint therethrough and onto the base. Since the base object is at a substantially lower tempera- 4 ture, the paint almost immediately freezes thereon. With the novel additive incorporated in the vehicles of the instant invention, a flatter print is obtained having fewer screen marks in the unfired condition. The paint containing the novel vehicle of the instant invention receives a second color without appreciable losses of detail from multi-color applications whether the second application is of the conventional or hot screen type. Examples of the vehicles employing the novel additive, specifically azelaic acid; 1,7-heptane dicarboxylic acid or nonanedioic acid, are as follows:

Example I A ceramic paste was compounded wherein the vehicle consisted of 65% stearic acid and 35% azelaic acid by weight. The paint was applied to a ceramic base object by means of the hot screen techniques wherein resistance heating of the screen was employed.

Example II A ceramic paint was compounded wherein the vehicle consisted of 60% stearic acid, 35 azelaic acid and 5% ethyl cellulose. The ethyl cellulose had an ethoxy substitution of from 47.5 to 49% and a viscosity of 10 cps. The ethyl cellulose was added as a viscosifier to impart added viscosity to the paint under the conditions of the application to a ceramic base according to the hot screen technique.

Example III A ceramic paint was compounded wherein the vehicle consisted of 60% stearic acid, 25% azelaic acid, 5% ethyl cellulose of the type set forth in Example II and 10% hercolyn. The hercolyn functions additionally to cause flow out of marks during the early stages of firing. The paste was then applied to a ceramic base object according to hot screen techniques wherein resistance screen heating was utilized.

Example IV A ceramic paste was compounded consisting of 35% stearic acid, 25 azelaic acid, 5% ethyl cellulose of the type set forth in Example If and 35% of behenic acid wherein the behenic acid had an behenic acid content and 15% stearic acid content. The behenic acid was 98.7% saturated. The paint was then applied to a ceramic base object by means of the hot screen squeegee process.

Example V A ceramic paint was compounded wherein the vehicle consisted of 75% AB acids, 22.5% azelaic acid and 2.5% ethyl cellulose of the type set forth in Exampl II. The AB acids were 97.7% saturated and were a mixture of the following acids: myristic 1.8%, palmitic 13.5%, stearic 17.2%, arachidic 38.3%, and behenic 29.2%. The paint was then applied to a ceramic paste object by means of the hot screen squeegee technique.

Example VI A ceramic paste was compounded wherein the vehicle consisted of 55% stearic acid, 10% azelaic acid, 5% ethyl cellulose of the type set forth in Example 11, 10% hercolyn, and 20% candelilla wax. This paste was applied to a ceramic object by means of the hot screen technique.

Example VII Another paste was compounded wherein the vehicle consisted of 65 stearic, 5% ethyl cellulose of the type set forth in Example ll, 10% azelaic acid, 10% hercolyn, and 10% stearyl stearate. The stearyl stearate had an .87% free fatty acid content and a melting point of 5 85 C. The stearyl stearate was added toirnpart desirable how and screening characteristics to theoil and paste. The paint paste was then applied to a ceramic object by means of the hot screen technique.

Example VIII A paint was compounded wherein the vehicle consisted of 60% stearic acid, 5% ethyl cellulose of the type set forth in Example II, azelaic acid, 10% hercolyn, 7%% stearyl stearate of the type set forth in Example VII, and 7V: behenyl behenate. Behenyl behenate had a .9% free fatty acid content and a melting point of 68 C. The stearyl stearate and behenyl behenate were added to impart desirable handling characteristics tothe paste. The paint was then applied to a ceramic object by means of the hot screen technique.

In each of the examples set forth, the print was flatter and showed fewer pronounced screen marks than customarily found with other known fatty acid type vehicles.

This application is a continuation-in-part of my prior application, bearing Serial No. 518,327, filed June 27, 195 5, now abandoned.

Having thus described the invention, what I claim is:

l. A homogeneous vehicle solid at room temperature for suspending a vitrifiable ceramic composition consisting essentially of a fundamental constituent in amounts in excess of about 35% by weight of the vehicle and azelaic acid in amounts from 0.5% to about 55% by weight of the vehicle, said fundamental constituent being selected from the group consisting of fatty acids having from 12 to 22 carbon atoms and mixtures thereof.

2. A homogeneous vehicle solid at room temperature for suspending a vitrifiable ceramic composition consisting essentially of a fundamental constituent in amounts in excess of about 35% by weight of the vehicle and '6 azelaic acid in amounts from 0.5 to about 55 by weight of the vehicle, said fundamental constituent being selected from the group consisting of lauric, myristic, palmitic, stearic, arachidic and behenic acids and mixtures thereof.

3,. A vehicle according to. claim 2 wherein said fundamental constituent is present in amounts ranging from about% to 95% by weight of the vehicle.

4. A vehicle according to claim 3 wherein ethyl cellulose is additionally present in amounts from about 1% to about 15% by weight of the vehicle.

5. A ceramic paste essentially consisting of a pigment and a homogeneous, thermoplastic vehicle solid at room temperature, said vehicle essentially consisting of a fundamental constituent in excess of 35 by weight of the vehicle and azelaic acid in amount from 0.5 to of the vehicle by weight, said fundamental constituent being selected from the group consisting of fatty acids having from 12 to 22 carbon atoms and mixtures thereof.

6. The invention as claimed in claim 5 wherein further, azelaic acid is present to the extent of from 10% to 35% by weight, said fundamental constituent is present to the extent of from to 50% by weight and is selected from the group consisting of lauric, myristic, palmitic, stearic, arachidic and behenic acids and mixtures thereof.

References Cited in the file of this patent UNITED STATES PATENTS UNITED STATES PATENT OFFICE CERTIFICATE OF CORRECT ION Patent No. 2,872,326 February 3 1959 William C. Morris s hereby certified that error appear-sin the-printed specification and that the said Letters 1 of the above numbered patent requiring correction Patent should read as corrected below.

Column 1, line 53, after "drying l insert prior Signed and seeled this 19th day of May 1959.

SEAL Attest:

KARL H... MINE Attesting Oflicer ROBERT C. WATSON Commissioner of Patents 

1. A HOMOGENOUS VEHICLE SOLID AT ROOM TEMPERATURE FOR SUSPENDING A VIRTRIFIABLE CERAMIC COMPOSITION CONSISTING ESSENTIALLY OF A FUNDAMENTAL CONSTITUENT IN AMOUNTS IN EXCESS OF ABOUT 35% BY WEIGHT OF THE VEHICLE AND AZELAIC ACID IN AMOUNTS FROM 0.5% TO ABOUT 55% BY WEIGHT OF THE VEHICLE, SAID FUNDAMENTAL CONSTITUENT BEING SELECTED FROM THE GROUP CONSISTING OF FATTY ACIDS HAVING FROM 12 TO 22 CARBON ATOMS AND MIXTURES THEREOF. 